The present invention relates to a method for constructing a model using computer assisted design and numerical control machine techniques wherein construction of the physical model is begun prior to completion of determination of surface data defining the completed model. The method of the present invention is particularly well adapted for making a model of an automobile body.
The design of an automobile body generally begins with a stylist's sketch of a shape which leads to the construction of a full scale stylist's clay model. The stylist's clay model provides a three-dimensional structure facilitating an appreciation of the esthetic appeal of the design which is difficult to fully appreciate from two-dimensional sketches or scaled down models. The stylist's model also provides a working medium allowing the addition of surface details and engineering development to meet fabricating and engineering requirements. Thus, after initial construction of the stylist's clay model, it is subjected to a substantial amount of analysis, evaluation and testing leading to the evolution of the final design. To facilitate the numerous changes made during this process, the stylist's clay model is made of relatively soft clay which is easily damaged and must be frequently repaired after being moved for wind tunnel testing or the like. Thus, once the stylist's clay model is refined to its final form, a more sturdy model, such as a wood model, is constructed for making dies.
It is known to use computers for the design and analysis of the surfaces which make up an automobile body. CAD/CAM (computer assisted design/computer assisted manufacturing) and N/C (numerical control) cutter techniques are now well known in the automobile and other industries and CAD/CAM and N/C hardware and software are readily commercially available. Early U.S. patents relating to the use of computer technology in automobile design include the Hart, et al. patent. U.S. Pat. No. 3,534,396, Oct. 13, 1970 to Hart, et al. teaches a method of analyzing and further developing graphical information utilizing digital computer in which information in a graphical form is translated into a form that can be accepted by a digital computer and is read into the computer in the translated form. The computer then translates the information into graphical form which can be viewed by an operation-designer who then modifies the graphical representation and feeds information into the computer in accordance with a modification or development of the information that is graphically displayed. When the operator-designer is satisfied with his design, the computer contains a representation of this design and the computer is capable of supplying a representation of the final design which then can be converted into various graphical forms such as a drawing. Another U.S. patent relating to numerically controlled surface development method for preparing automobile body contours is U.S. Pat. No. 3,548,173 Dec. 15, 1970 to Pascoe et al. The Pascoe, et al. patent relates to methods for determining analytically the geometric characteristics of an automobile body and subsequently using the analytical data for a numerical control system for a machine tool such as a multiple axis milling machine.
Present design and model making techniques generally involve a sequential procedure wherein surface data is first fully processed to high density data in the computer and then the data is used to drive an N/C mill or cutter. In the automotive field, a full size clay model is constructed, then the geometric data defining the body contours of the clay model is fed into a computer, smoothed and sweetened, evaluated for compatibility with engineering and fabrication requirements, welding points, internal structure, and so forth, and subsequently utilized to make models of the automobile body parts using N/C techniques. The geometric data is not obtained until the design of the clay model is essentially complete. The construction of the wood models does not begin until the geometric data has been processed and analyzed by the computer. The sequential nature of this design procedure is time consuming and requires that the final body contour design be well established before construction of the wood models can begin.
The method of the present invention is an improvement over the above-mentioned procedure wherein CAD/CAM and N/C machine techniques are employed in a manner which shortens the time and lowers the cost for making a model. Thus, in accordance with the present invention, a sturdy three-dimensional master model is constructed using CAD/CAM and N/C machine tool techniques by digitally processing surface data to obtain low density, unsweetened, template contour lines offset below the desired surface on an axis normal thereto, and then simultaneously constructing a rough model having a surface offset above the desired surface on an axis normal thereto, while developing the low density surface data to sweetened, high density cutter path data and then using the cutter path data to N/C mill the rough model to the desired surface.